1. Field of the Invention
The present invention relates to a tissue imaging system and in vivo monitoring method. More particularly, the present invention relates to a tissue imaging system and in vivo monitoring method in which oxygen saturation of body tissue in a body cavity is monitored with high stability even upon incidental shift of a field of view of an imaging instrument for imaging of by body tissue.
2. Description Related to the Prior Art
JP-A 2000-139947 discloses percutaneous treatment (laparoscopic surgery) of a patient's body by use of a laparoscope. In the percutaneous treatment, two or three holes are formed in skin outside an abdominal cavity. The laparoscope and a medical instrument for operation are inserted in the holes into the abdominal cavity. The abdominal cavity is insufflated with gas, such as carbon dioxide gas. A doctor or operator observes an image in the abdominal cavity by use of a monitor display panel, and carries out the percutaneous treatment by use of the medical instrument. The percutaneous treatment is characterized in that the view of field of imaging in the laparoscope is limited considerably, so that the doctor or operator must have a high technical skill. There is an advantage in the percutaneous treatment in that physical stress to the patient is very low, because it is unnecessary to incise the abdominal cavity surgically.
A low oxygen environment is likely to occur with blood vessels in the abdominal cavity because carbon dioxide gas is used in the percutaneous treatment for insufflating the abdominal cavity. In case of the low oxygen environment, the percutaneous treatment is interrupted to start surgical operation. It is necessary in the percutaneous treatment to monitor an oxygen saturation in blood of the blood vessels.
Various methods of monitoring the oxygen saturation are known. In a first one of the methods, a measurement probe is held manually with fingers of a doctor or operator, and measures the oxygen saturation percutaneously. A second one of the methods is disclosed in a relevant website, http://www.spectros.com/products/t-stat-ischemia-detection/about-t-stat/system-overview.html (found on 12 Nov. 2010) in which a non-contact measurement probe is advanced through an instrument channel in the laparoscope, and measures the oxygen saturation of the blood vessels in a non-contact manner. The non-contact measurement probe applies measuring light of a predetermined wavelength to the blood vessels, and receives the light reflected by the blood vessels by use of a CCD image sensor or the like. The image sensor generates an image signal according to which the oxygen saturation of the blood vessels is determined.
Specifically in an artery bypass operation in the percutaneous treatment, it is possible in the non-contact measurement probe of the above-indicated relevant website to monitor changes in the oxygen saturation with time of the blood vessels important surgically (for example, aorta and coronary artery), for the purpose of safety in the percutaneous treatment. However, the above-indicated relevant website discloses measurement in a protruding state of the non-contact measurement probe from a tip of the laparoscope. Should motion occur with the tip of the laparoscope incidentally or in the course of the treatment, there occurs a shift in the position of the non-contact measurement probe. Measuring light from the non-contact measurement probe cannot be sufficiently applied to the blood vessels to be monitored upon occurrence of the shift of the non-contact measurement probe. The oxygen saturation of the blood vessels cannot be exactly determined due to the incidental shift of the non-contact measurement probe.